There has been a continuing need for an economical method of preparing isocyanatoorganosilanes, including isocyanatoalkylsilanes, in high yields and purities from relatively non-hazardous raw materials. Heretofore, isocyanatoorganosilanes have been made in relatively low volumes by inefficient or costly processes.
For example, isocyanatoorganosilanes have been prepared by processes involving the addition of hydrosilanes to unsaturated isocyanates, particularly allyl isocyanate, in the presence of a noble metal catalyst. Allyl isocyanate is a highly toxic raw material of limited commercial availability.
Processes also are known wherein isocyanatoalkylsilanes are prepared from carbamatoalkylsilanes at low temperature in the liquid phase, or from aminoalkylsilanes and highly toxic phosgene by various routes. All liquid phase processes disclosed thus far suffer from one or more disadvantages of low yield, slow kinetics, need for highly toxic raw materials, need for extensive work-up or purification, often in the presence of higher levels of close-boiling contaminants, and substantial generation of by-products and waste materials.
High temperature, vapor phase processes are also known; but these generally require specialized equipment capable of high temperature operation, with concurrent extensive capital investment. A method for making 2-isocyanatoethoxysilanes by liquid phase thermal rearrangement of N-silyl-2-oxazolidinones has also been disclosed. The bonding of the isocyanatoalkyl groups to silicon atoms in these molecules is through hydrolyzable silicon-oxygen bonds, and the silane moiety does not contain additional alkoxy groups as are present and often necessary in current commercially useful isocyanatoalkylsilanes.